Semiconductor device and camera using same

Abstract

The present invention provides a semiconductor device that can adjust signal frequency bandwidths and consumption currents to be appropriately increased or reduced in source-follower amplifiers in all stages. The semiconductor device is comprised of a source-follower amplifier including a driver transistor D 1 , and a load transistor L 1 that is connected to the driver transistor D 1 and driven variably depending on a signal inputted to the driver transistor, wherein a gate of the load transistor L 1 is applied with a variable bias voltage. The semiconductor device 1 is further comprised of a source-follower amplifier including a driver transistor D 2 , and a load circuit (load transistor L 2 ) that is connected to said second driver transistor and driven variably depending on a signal outputted from the second driver transistor D 2 , wherein a gate of the load transistor L 2 is applied with a variable bias voltage to vary a resistance value of the load transistor L 2.

What is claimed is: 
     
       1. A semiconductor device, comprising:
 an initial-stage source-follower amplifier including a first driver transistor, and a first load transistor that is connected to said first driver transistor and driven variably depending on a signal inputted to said first driver transistor; and 
 a final-stage source-follower amplifier including a second driver transistor, and a load circuit that is connected to said second driver transistor and driven variably depending on a signal outputted from said second driver transistor, 
 wherein a gate of said first load transistor is applied with a variable bias voltage, and said load circuit is applied with a variable control voltage to vary a dynamic resistance value of said load circuit, 
 wherein said load circuit includes a plurality of second load transistors that are connected in parallel to each other, and 
 wherein respective gates of said second load transistors are applied with respective variable bias voltages to vary respective resistance values of said second load transistors. 
 
     
     
       2. The semiconductor device according to  claim 1 , further comprising
 a source-follower amplifier that drives said final-stage source-follower amplifier variably depending on a signal outputted from said first driver transistor, said source-follower amplifier being placed between said initial-stage source-follower amplifier and said final-stage source-follower amplifier. 
 
     
     
       3. A camera, comprising
 the semiconductor device according to  claim 2 . 
 
     
     
       4. A camera, comprising
 the semiconductor device according to  claim 1 . 
 
     
     
       5. A semiconductor device, comprising:
 an initial-stage source-follower amplifier including a first driver transistor, and a first load transistor that is connected to said first driver transistor and driven variably depending on a signal inputted to said first driver transistor; and 
 a final-stage source-follower amplifier including a second driver transistor, and a load circuit that is connected to said second driver transistor and driven variably depending on a signal outputted from said second driver transistor, 
 wherein a gate of said first load transistor is applied with a variable bias voltage, and said load circuit is applied with a variable control voltage to vary a dynamic resistance value of said load circuit, 
 wherein said load circuit includes a second load transistor and a constant current circuit that are connected in parallel to one another, 
 wherein a gate of said second load transistor is applied with a variable bias voltage to vary a resistance value of said second load transistor, and 
 wherein said constant current circuit is applied with a variable control voltage to vary a dynamic resistance value of said constant current circuit. 
 
     
     
       6. The semiconductor device according to  claim 5 ,
 wherein said load circuit is placed outside of said semiconductor device. 
 
     
     
       7. A camera, comprising
 the semiconductor device according to  claim 6 . 
 
     
     
       8. The semiconductor device according to  claim 5 ,
 wherein said constant current circuit includes a constant current device and a resistance device that is connected to said constant current device, and 
 wherein said constant current device is applied with the variable control voltage to vary the dynamic resistance value of said constant current circuit. 
 
     
     
       9. A camera, comprising
 the semiconductor device according to  claim 8 . 
 
     
     
       10. The semiconductor device according to  claim 8 ,
 wherein said constant current device is a bipolar transistor. 
 
     
     
       11. A camera, comprising
 the semiconductor device according to  claim 10 . 
 
     
     
       12. The semiconductor device according to  claim 8 ,
 wherein said constant current device is a MOS transistor. 
 
     
     
       13. A camera, comprising
 the semiconductor device according to  claim 12 . 
 
     
     
       14. The semiconductor device according to  claim 8 ,
 wherein said resistance device includes a plurality of resistance elements, and 
 wherein a resistance value of said resistance device varies by selecting one of said resistance elements to be used. 
 
     
     
       15. A camera, comprising
 the semiconductor device according to  claim 14 . 
 
     
     
       16. A camera, comprising
 the semiconductor device according to  claim 5 . 
 
     
     
       17. The semiconductor device according to  claim 5 , further comprising
 a source-follower amplifier that drives said final-stage source-follower amplifier variably depending on a signal outputted from said first driver transistor, said source-follower amplifier being placed between said initial-stage source-follower amplifier and said final-stage source-follower amplifier.